Means for compounding voltage regulators for three-phase generators



Feb. 28, 1933. 1,899,406

mums FOR COIPOUNDING VOLTAGE REGULATORS FOR THREE-PHASE eauzauons A. YTTERBERG 1931 2 Sheets-Sheet 1 Filed July 14 1? V6)? for fir/e Yfferb erg;

Feb. 28; 1933. YTTERBERG 1,899,406

MEANS FOR COIPOUNDING VOLTAGE REGULATORS FOR THREE-PHASE GENERATORS Filed July 14, 1931 2 Sheets-Sheet 2 c K c c ii? I 2 x 'kii gg 1 x J11 yen for file Yzierber fifomex Patented Feb. 28, 1933 UNITED STATES PATENT OFFICE,

ABLE YTTERBERG, OF HOGBERGET, LUDVI'KA, SWEDEN, ASSIGNOR TO ALLMKNNA SVENSKA ELEKTRISKA AKTIEBOLAGET, OF VASTERAS, SWEDEN, A CORIPORATION OF SWEDEN MEANS FOR COMPOUNDING VOLTA GE REGULATORS FOR THREE-PHASE GENERATORS Application filed July 14, 1931, Serial No. 550,733, and in Sweden July 15, 1930.

When the voltage in an alternating current system sinks considerably on account of a short-circuit there is always a risk of synchronous motors connected to the system falling out of step andof the speed of asynchronous motors sinking below that corresponding to maximum torque, whereby the overload spreads over larger and larger portions of the system. When the short-circuit is a symmetrical three-phase one, by compounding the voltage regulators of the generators, the voltage in the major portion of the system may be kept'at a reasonable value without great difliculty even on the occasion of a local short-circuit. Most short-circuits are, however, more or less unsymmetrical, so that the voltages on the different phases will also be unsymmetrical. The condition whereby the torque of a motor connected to the system at a certain point shall'not sink below normal will, in this case, as the theory shows, be such that the so called right-way voltage star at this point retains its normal value. In any unsymmetrical polyphase alternating current system the different factors (voltage, current etc.) can be divided into one right-way and one reverse portion, which in transition to singlephase will be equal. The expressions in question involve that the phase sequence in one case is normal, and in. the other case contrary to the normal one. If. for instance. the three line conductors are designated by I, II, III and, under normal. conditions, the voltages between the difi'erent conductors and the neutral point reach their maximum values in the order determined by the said numbers, this will also be the case for the right-way component of an unsymmetrical voltage system, while the mutually equal voltages which form the reverse component will reach their maximum values in the different conductors in the time sequence I, III, II.

The object of the present invention is to accomplish in a simple way such a compounding of the voltage regulators for threephase generators that at any point of the network the right-way voltage system can be kept at a substantially constant value also on the occasion of an unsymmetrical shortcircuit.

In the accompanying drawings Fig. 1 shows a vector diagram illustrating the method of deriving, from an unsymmetrical threephase current start, its two symmetrical components. Fig. 2 shows another vector diagram illustrating the derivation of the induced voltage of a generator from a terminal voltage vector and two current vectors for unsymmetrical load. Figs. 3-6 show finally four examples of compounding impedances according to the invention for unsymmetrical load, founded on the aforesaid diagrams.

In Fig. 1 of the drawings, I I I represent three unsymmetrical currents in a threephase line, the vector sum of which, however, is assumed to be zero, so that no current exists through the neutral point. For dissolving such a vector star in its symmetrical right-way and reverse components, I may for instance be rotated through an angle of 30 in the direction of the phase sequence and I through an equal angle opposite to the said direction and the vectors thus rotated combined to a resultant vector L. For the reverse vector star this will mean the same as arotation of the preceding vector in the phase sequence through 30 against the phase sequence and of the succeeding vector through 30 in the direction of the phase sequence, which means that the vectors which originally form 120 with one another will form an angle of 180 and their resultant thus be zero. The resultant I just derived will therefore only contain the components of the right-way vector star. Its magnitude will be determined by the fact that the angle between the said components is only instead of normally 120 which implies that the resultant vector must be divided by in order to give a correct value of the components. The phase of the resultant is in the symmetrical vector star midway between those of the components and thus directly opposite the right-way component of 1,. The

said component 1 can thus be drawn right opposite to the resultant L and equal to between L} and L =l and the vector diiier ence between 1 and I =l are derived. It 18 then found that the three vectors l L L form a symmetrical star with the phase sequence opposite to that of the original vec tors which is a criterion of the correctness or" the method employed.

7 rive the induced machine voltage (depending It can be easily. demonstrated that the right-way voltagestar at any point oithe network depends only on the originally in.- duced symmetrical machine voltage and the voltage drops produced by the right-way current star. I In order to keep the rightway voltage star constantat any point of the network, it is therefore only necessary to compound the. induced voltage-tor this voltage drop. When the machinevoltage is regulated by a voltage regulator connected to the machine terminals in series a ith so called compounding impedances, the matterwill, however, not be quite so simple for the reason that'the voltagebetween the machine terminals is not the induced voltage but contains also the voltage drop in the machine,

which is unsymmetrical to the same extent as the voltage drop ln'the lines. In order to de on the .air gap fluX),,-thevoltage regulator must first be negatively compounded for the Voltage c rop in the machine. This is accomplished accordingtothe principle illustrated in Fig. 2. if the induced machine in this figure are E E E the induced voltage between the phases 2 and. 3 'willhe E The currents l an-dL which are assumed to have the same magnitude and'phase asjin Fig.1 will cause'in their respective windings voltage drops E -.12 which for the sake of simplicity maybe assumed to be purely inductive and thus perpendicular to the currents. The resultant terminal voltage will be E, and this voltage is obtained in voltages' trated in Fig. 1. These impedances, in practice, since they should also be traversed by the currents from the phases 2 and 3, may be combined with the former ones in a common apparatus, the adjustment of which for different compounding may be accomplished for instance by means of a line diagram.

in Fig. 3 of the drawings, 1, 2, 3 designate,

the three phases of a threephase generator and'O its neutral point. Between the phases 2 and 8, there is connected a voltage transformer V, and in the conductors from the said phases there are inserted current trans formers C 0 These operate a compounding impedance K which is partly common to both andconsists ofself inductance K and ohmicresistance K;,'the whole being so arrangedthat the currents, are combined according to theprinciple illustrated in Fig. l and a voltage proportional to the resultant and underanappropriatephase angle against the latteris obtained. If it is assumed, for V spective directions through 30, because this resultant-is perpendicular to the voltage be tween the phases 1 and 2it the current and voltage are in phase. H In this case it is therefore only necessary to' arrange in such a way thatthe impedances of the two current paths are numerically equal and their phase angles are +30 for. one impedanceand -30 for the other.- The phase angle of an impedance is defined as the phaseangle between the voltage between its terminals and the current traversing the impedance. Generally speaking,the impedances of the two current pathsshall'be numerically equal and possess phase'angleathe difterenceof which is 60. By means of. an adjustable transformer T, the exciting current or which is delivered by a condenser F, the numerical value of the additional voltage may be accurately regulated. This, additional voltage is finally combined with the voltage from the .transit'ormerV and impressed-on the regulator R;

In Fig. 3 there is alsoshown another compounding device which in some cases is necessaryor desirable. If the vector sum of the currents in thethree phases is not zero, a current flowsalso through the neutral point and is generally equally distributed between the three phases. These currents do not cause any voltage dropin its proper sense, that is, a reduction ofthe right-way voltage star at any point of the network, but only a displacement of the neutral point of the said star in relation to that of the generator. Since they 7 impedance K is, traversed by the currents in two phases, the voltage produced thereby will, however, contain a component proportional to the neutral point current which anust be compensated in order to cause the voltage regulator to produce the desired voltage on the machine. For this purpose the current between the generator neutral point 0 and the earth J will influence a compounding impedance K dimensioned so as to compensate the aforesaid undesirable voltage component.

In Fig. 3 no respect has been paid to the voltage drops in the generator itself. Fig. 4 on the contrary, shows an arrangement for this purpose, founded on the diagram shown in Fig. 2. The regulator and the voltage and current transformers are here designated in the same way as in Fig. 3 but the compounding impedance is designated by K and is assumed to be so dimensioned as to produce two voltage components according to Fig. 2. As the impedances necessary for this purpose always shouldbe the same for a given machine, a particular transformer for regulating the numerical value is superfluous.

Fig. 5 shows an example of the complete compounding diagram for a power station having two generators vand an outgoing line. For each generator there is here provided a compounding impedance K for compounding inwards to the induced voltage, an impedance K for compounding for the voltage drop in the connections between the generator and the bus bars including a transformer therebetween, and an impedance K for compounding for the voltage drop in the line. The impedance K as well as the impedance K are fed from current transformers C and the former one is preferably so dimensioned as to leave a small portion of the voltage drop uncompensated for effecting stability between the generators. The inipedance K, is fed by current transformers C in the line and should of course, for the delta-star connection of the power transformer shown, be dimensioned in a corresponding manner, so as to give the correct phase of the additional voltage. Otherwise the same reference letters designate the same parts in this figure as in Fig. 3.

The compounding impedances K and K may be combined into one if desired, but the division into two has among others the advantage that the regulation will be more simple, for instance if it is desired to parallel the generators directly instead of through transformers. The impedance K may then simply be adjusted to zero value. K, may also be combined with a sufiicient portion of K for compounding substantially to the generator terminals for the right-way symmetrical load. A small portion of the voltage drop caused hereby should, however, always remain for stabilizing purposes.

Fig. 6 shows a particular form of such compounding impedances K, which should be capable of regulation in magnitude and/or phase, such regulation being very easily accomplished in this arrangement. As aforesaid, the difference between the phase angles of the two impedances should be 60. Now, if the phase angle of one of said impedances is 15 and of the other the phase angle of their resultant will be 45, as they are equal in numeric value. This will mean that if an impedance P containing numerically equal resistance P. and reactance P is connected in parallel to K the voltage on one of these latter components will be exactly in phase and on the other exactly in quarter-phase with the current. By adjustable taps on these two components the desired voltage is therefore very easily obtained without the use of any diagram. Otherwise the reference symbols in this figure correspond to those of Figs. 3 and 5.

I claim as my invention:

1. In voltage regulators for threephase generators, a threephase generator, a voltage regulator and compounding impedances connected in series between two terminals of said generator, said impedances being numerically equal but differing in phase angle by 60, and current transformers adapted to force currents proportional to the currents flowing out from said two terminals to flow through said impedances.

2. In voltage regulators for threephase generators, a threephase generator, a. voltage regulator and compounding impedances connected in series between two terminals of said generator, two of said impedances being numerically equal but differing in phase angle by 60, two other of said impedances being mutually equal in numerical value as well as phase angle and corresponding to the impedances in the machine, and current transformers adapted to force currents propor tional to the currents flowing out from each of said two terminals through one of each of said pairs of impedances.

3. In voltage regulators for threephase generators, a threephase generator, a voltage regulator and compounding impedances connected in series between two terminals of said generator, two of said in pedances being nu merically equal but differing in phase angle by 60, current transformers adapted to force currents proportional to the current flowing out through said two terminals to flow through said impedances, and a current transformer adapted to force a current proportional to the current flowing between the generator neutral and earth through one of said compounding impedances.

4. In voltage regulators for threephase generators, a threephase generator, a voltage regulator, two impedances having phase angles of respectively 15 and 75, current transformers adapted to force currents proportional to the currents flowing out from two terminals of said generator through said impedances, and an impecance consisting of numerically equal resistance and reactance (Lil connected in parallel to said impedances, adjustable portions of said last mentioned impedance being connected in series With said voltage regulator between said generator tel minals.

7 In testimony whereof I have signed my name to this specification.

ABLE YTTERBERG. 

